The present invention relates to an automatic sheet feeder usable with an image recording apparatus, such as an electrophotographic copying machine, a microfilm machine, a facsimile machine and a printing machine, e.g., a laser beam printer and an ink jet printer. More particularly, it relates to an automatic sheet feeder which can process a sheet while it is being advanced. Further, it relates to an image recording apparatus provided with such an automatic sheet feeder. In this invention, the term "sheet" includes a sheet-like member, such as a document and a recording card, having information to be recorded.
As a typical example of a circulation type sheet feeder, there is an automatic sheet document feeding device of a circulation type (RDF) used with an image forming apparatus, such as a copying machine. For the better understanding of the present invention, the document feeder of this type will be explained.
FIG. 1 schematically shows the document feeder B mounted to the top panel 102, having a platen glass 101, of a copying apparatus A.
The document or original feeder B is provided with a tray 110 for stacking sheet originals, which functions as a sheet stack portion. On the tray 110, one set of sheet originals O each having the information to be recorded on its one side, is placed. The originals O are stacked face up on the tray in the order of the page number from the top. In operation, the bottommost original in the stack on the tray 110, upon the copy start instructions, is fed out by a sheet separator mechanism 111 into a first sheet passage 112, and guided to the left hand side of the platen glass 101. Then, the original is guided so as to face down between the platen glass 101 and a flat surface of an endless belt 113 for feeding the original, the flat surface being press-contacted to the top surface of the platen glass 101 and being driven in a forward direction a. The original is driven by the flat surface of the belt 113 so as to slide on the platen glass 101 from the left-hand side to the right-hand side in the Figure. The movement of the belt 113 is stopped at the time when the left hand edge of the original reaches a reference line 101" on the platen glass 101. By this, the original is automatically advanced and set at the predetermined position on the platen glass 101.
When the belt 113 stops, a movable optical system 103 of the copying machine A is driven to optically scan the bottom side of the original stationarily set on the platen glass 101. The scanned image is projected through a slit and imaged onto a surface of a rotatable photosensitive member or drum 109. A copy of the original or document is produced with the cooperation of the other copy process means.
When the scanning operation of the movable optical system 103 for the original on the platen glass 101 completes, the belt 113 is driven in the backward direction b, so that the original on the platen glass 101 which has been copied slides back leftwardly on the platen glass 101 by the backward driving force of the belt 113 and is guided to a second sheet passage 114. Through the sheet passage 114, the original is returned on the tray 110 through the original discharging portion 115 which is located above the sheet separator mechanism 111. The original is discharged onto the topmost original (the first page of the set of originals) of the stacked originals O. At this time, it will be understood that the returned original faces up.
On the other hand, the original on the tray 110 which is then bottommost is introduced to the first sheet passage 112 by the sheet separator mechanismm 111. Before the leading edge of the original reaches the left-hand end of the contact area between the platen glass 101 and the flat surface of the belt 113, the rotation of the belt 113 is switched to the forward movement. The original is advanced rightwardly on the platen glass 101 by the moving flat surface belt 113. Similarly to the previous original, this original is stopped at the predetermined position and is subjected to the optical scanning operation, and then the original is returned by the reverse rotation of the belt 113 until it is discharged.
The above-described process from the feeding to the discharging of the original is effected to the individual originals stacked on the tray 110. When all of the stacked originals are thus circulated once for each, one set of copies of the stacked originals is produced. If the cycle is repeated, a desired number of sets can be obtained. Thus, this system is advantageous in that it can automatically and quickly produce copies of a great number of sheet originals.
The movable optical system 103 of the copying machine A comprises a lamp 104 for illuminating the original, a first movable mirror 105, a second movable mirror 106, an imaging lens 107, a fixed mirror 108 and others. Of these elements, the lamp 104, the first movable mirror 105 and the second movable mirror 106 are normally placed at their home positions in the neighborhood of the left-hand end of the platen glass 101 as viewed in the Figure, as shown by the solid lines in FIG. 1. However, upon the generation of an optical system starting signal, the lamp 104 is energized, and the lamp 104 and the first mirror 105 are advanced at the same speed as the peripheral speed of the photosensitive member 9, while the second mirror 106 is moved at half that speed. Those are moved rightwardly along the bottom surface of the platen glass 101 and are reciprocated. By the movement of the optical elements, the image or information on the bottom surface of the original supported on the platen glas 101 by the circulation type document feeder B, is optically scanned from the left-hand side to the right-hand side. When the lamp 104, the first mirror 105 and the second mirror 106 reach their reversing points as shown in the Figure by the chain lines, the lamp 104 is de-energized, then those elements are reversed to reach the respective home positions and are prepared for the next starting instructions. It is a possible alternative that the optical scanning is effected not during the forward movement of the optical system, but during the returning movement thereof.
As for the sheet separator mechanism 111 for feeding out the sheet originals one by one, various types and mechanisms are usable. The apparatus shown here employs a mechanism comprising in combination a sheet feeding belt 116 moving co-directionally with the sheet original feed and a sheet separating belt 117, disposed above said sheet feeding belt 116, which moves counter-directionally with the sheet feed. Detailed explanations as to the principle of the sheet separation are omitted for the sake of simplicity, since it is well-known.
The circulation type document feeder B includes an outer casing 118, a roller 119 for driving the belt 113, a turning roller 120 and urging rolls 121 for urging the flat face of the belt 113 onto the platen glass 101 in a proper pressure to increase the feeding force to the original imparted during the forward rotation of the belt 113. The original stacking tray 110 is inclined at an angle of approx. 20 degrees downwardly toward the sheet separator mechanism 111.
The document feeder B is pivotable toward and away from the platen glass 101 by a hinge (not shown) provided at the rear side thereof. When an original which is not suitable for the document feeder, such as a thick original like a book, is to be copied, the entire document feeding device is pivoted away from the platen glass 101, and the original is placed face down on the platen glass 101, whereafter the document feeder B is pivoted toward the original to urge the original toward the platen glass 101 so that the document feeder B functions as an original cover on that occasion.
It is possible that the document feeder B is equipped with a mechanism for reversing and re-introducing the original to the platen glass 101 so as to make it possible to obtain a duplex copy. In order to increase the speed of the copying operation in the copying apparatus equipped with the document feeder B, the following measures, for example, are considered:
(1) As for the document feeder B, the speed of the original movement from the tray 110 to the predetermined position on the platen glass 101 and the speed of the original movement, after the scanning, from the platen glass 101 to the tray 110, are increased as much as possible:
(2) As for the copying machine A, the speed of the movement of the optical system 103 to the home position is increased as much as possible.
Those measurements are, in effect is to reduce the time spent not for the step directly concerned with the actual formation of the image, which is contained in one copying cycle from the start of the original feed from the tray 110 to the discharging of the copy thereof to a copy tray (not shown) of the copying machine A. However, there is a limitation to the increase of the speed as stated in the above item (1) since the increase may result in a damage to the originals. As for the above item (2), there is a liability of adverse effects to the other parts of the apparatus, since it may result in an increased mechanical load, and therefore, a stopping shock and vibrations.